Part 2 differences from the book

Under the page for Harry Potter and the Deathly Hallows Part 2, under the section Differences from the book, it says that the statues and armor will come to life and fight for the school. I can't understand why this is a difference when, I remember cleary in the book Professor McGonagal bewitching them to come to life and ordering them to protect the school, screaming "Hogwarts is threatened!" So this did happen in the book and even other sites are claiming that it was put in for the movie! Can somebody please clear this up for me?